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Design-in Guide - Philips Xitanium LED Xtreme SR driver
Relation between t
and ambient temperature
c
The t
increases, by approximation, linearly with the driver ambient
c
temperature (t
). The temperature offset between driver t
a
depends on the thermal design of the luminaire and the actual
delivered output power relative to the specified nominal
output power. A lower output power allows for a higher
driver ambient temperature as long as the maximum specified
driver t
is not exceeded. For the approved driver ambient
c
temperature range as well as specified t
check the specific driver datasheet.
Note:
The specified t
(max) and minimum t
c
not allowed to be exceeded in the application; otherwise driver
warranty will be void and driver failure rate will increase.
ThermalGuard
In a thermally well-designed lighting system the specified t
value will not be exceeded. However, under extreme
application conditions the driver may occasionally overheat. In
that
case
the
driver will automatically start to reduce the
output current as an emergency measure in order to reduce
excess heat generation in the LED module and in the driver
itself. The result of the output current reduction will be a
mitigation of the excess decrease of driver lifetime as a result
of thermal overstress. Once the t
dropping the driver will automatically increase the output current
up to the pre-set output current.
If the output current reduction is not sufficient to offset the t
temperature increase then the output current may either stabilize at
a lower value or –depending on driver type- even be reduced to
zero in extreme cases.
This thermal driver protection feature is called ThermalGuard and
its goal is to get the driver back in normal operating thermal
conditions in which the specified driver lifetime can be met. Each
driver type has its own specific overheating behavior and it can be
found as a ThermalGuard graph in the driver datasheet. The
ThermalGuard feature can neither be disabled nor reconfigured.
Note: the ThermalGuard feature is designed as a non-
configurable emergency measure to protect the driver. It is not
intended for structural activation to compensate for a poor
thermal design of a lighting system.
and t
a
point values please
c
temperature limit values are
a
(max)
c
hot
point temperature starts
c
point
c
12
c
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